Field emission display technology may be used in a wide variety of applications including flat panel displays. The technology involves the use of an array of field emission devices. Each field emission device has an anode, cathode, and gate. Each field emission device cathode includes a microtip for emitting electrons. The fabrication of field emission device cathodes requires multiple steps. These fabrication steps are complex and require expensive materials and equipment. The fabrication steps also require a high degree of precision.
One common technique for fabricating cathode microtips involves high-angle evaporation of a sacrificial or "lift-off" layer followed by vertical evaporation of the microtip metal. The sacrificial layer is formed on top of the gate and on the edges of an opening in the gate. The openings in the gate begin to become restricted as the sacrificial layer is applied. As the microtip is formed through the opening and inside a cavity, the evaporated microtip metal also builds up on top of the sacrificial layer. The sacrificial layer, along with all of the overburden or subsequent microtip metal layers, is later "lifted-off" to preserve the underlying microtip and structure. The deposition and removal of this sacrificial layer is demanding and critical to proper device operation. One common technique of high-angle evaporation of a sacrificial layer is known as nickel evaporation in which a nickel layer serves as the sacrificial layer. However, the nickel layer tends to grab onto the gate layer, resulting in low reliability of the "lift-off" technique.
Another technique for applying a sacrificial metal layer is electroplating. One technique of electroplating is known as nickel electroplating. Nickel electroplating involves the application of a nickel layer to serve as the sacrificial layer during the fabrication of the cathode microtips. Just as in nickel evaporation, the sacrificial layer protects the integrity of the underlying microtip and structure. The sacrificial layer, along with all of the overburden, is later removed in the "lift-off" process. Nickel evaporation and nickel electroplating are expensive, time consuming, technically challenging, and sometimes unsuccessful. Further, the "lift-off" process does not always provide the desired separation of the nickel layer from the gate layer in order to expose the microtip.
Current techniques for fabricating cathode microtips use expensive refractory metals such as niobium and molybdenum. These refractory metals have a high melting point which is necessary when fabrication techniques such as high-angle evaporation are used. In order to conserve expensive refractory metals, the microtips are made smaller. Accordingly, the openings in the gate leading to the microtip must also be smaller and require the use of an expensive, high precision stepper to fabricate the openings in the gate.